High-resolution Spectroscopy of CARMENCITA objects Patrick Schöfer 2015-10-22
Overview Motivation Aims of the analysis and data sample Prelude I: Data reduction Prelude II: Target identification Analysis and results: Radial velocity Spectral type Activity Summary
Motivation What is CARMENCITA? [http://hades.fis.ucm.es/ carmencita/db.php] CARMENES Cool dwarf Information and data Archive CARMENES input catalog What is CARMENES? Calar Alto high-resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs German-Spanish collaboration [http://carmenes.caha.es/]
Motivation Radial velocity method: planet and star moving around center of mass different Doppler shifts visible in spectrum
Motivation radial velocity semi-amplitude K: Earth around Sun: K = 0.09 m s -1 below current detection limit planet with M P = 2 M in liquid water zone of M5 dwarf (T = 3050 K, M = 0.2 M ): K = 1 m s -1 RV method requires high-precision radial velocity measurements
Motivation Limitations set by the telescope: only stars with declination δ > -23 observable J magnitude < 11.5 mag (lower for earlier types) Limitations set by the method: no close binary stars (additional RV variation) no active stars (artificial RV variations caused by starspots, broad lines due to fast rotation)
Aims of the Analysis and Data Sample measure radial velocities to find expectation values and large variations (binaries) find active stars using the Hα line as activity indicator
Aims of the Analysis and Data Sample 1700 spectra 521 stars (480 CARMENCITA objects) 3 spectrographs (CAFE, FEROS, HRS) Telescope Res. Power R λ Range [A ] # Spectra CAFE 2.2 m Calar Alto 62,000 3960:9500 903 FEROS 2.2 m ESO, La Silla 48,000 3600:9200 640 HRS 9.2 m HET, Texas 60,000 4200:11000 157 85 stars observed with two spectrographs
Prelude I: Data Reduction 2D échelle spectrum 1D merged spectrum elimination of instrumental effects
Prelude I: Data Reduction 256 CAFE spectra in raw format REDUCE (Piskunov & Valenti, 2002) basic image processing order tracing in flatfield need to increase contrast FOX (Zechmeister et al., 2014) wavelength calibration manual identification of first lines normalization using continuum of reference star (no continuum in M dwarf spectra)
Prelude II: Target Identification comparison of CAFE FITS headers with hand-written logs wrong coordinates for 58 spectra coordinates between observed target and next target written after telescope started moving!
Prelude II: Target Identification no major problems with FEROS spectra wrong coordinate system given in HRS FITS headers, different naming convention, but no major problems
Prelude II: Target Identification Other problems found: typographical errors (usually easy to find and fix) only Jhhmms instead of full CARMENCITA identifier Jhhmms+DDd (ambigous in some cases) confusion with a nearby star (noticed during analysis)
Radial Velocity radial velocity V r given by Doppler shift cross-correlation of 3-5 wavelength ranges between 6200 A and 8600 A with a synthetic PHOENIX spectrum Gaussian fit to most significant peak in crosscorrelation function average of V r corresponding to valid Gaussian fits barycentric correction weighted average if a star was observed more than once
Radial Velocity Radial velocities of 79 single stars observed with two spectrographs good agreement overall significant outliers are active stars
Radial Velocity Comparison of results for non-carmencita objects with literature significant outliers are spectroscopic binaries RMSD = 0.69 km s -1 (without binaries)
Radial Velocity Comparison of results for CARMENCITA objects with literature Lam14: same spectra, same method, but erroneous barycentric correction New14: no trend PMSU: accuracy ~10 km s -1 others: outliers are active stars Lam14: Lamert (2014); New14: Newton et al. (2014); PMSU: Palomar/Michigan State University Survey
Radial Velocity 11 stars with significant RV variation over time SB1 candidates probably more in the sample, because 258 stars were observed only once 33 stars with more than one significant peak in the cross-correlation function SB2 candidates 10 new SB1, 23 new SB2 candidates
Radial Velocity Summary: matching results from different spectrographs accuracy ~ 1 km s -1 results for CARMENCITA objects more accurate than previous work 44 spectroscopic binary candidates among CARMENCITA objects, 33 of them new
Spectral Type spectral indices converted to spectral type using calibration data from THE HAMMER (Covey et al., 2007) and linear interpolation average of several spectral indices sensitive for M dwarfs (e.g., Ca I, TiO, VO) first estimate using 3 indices different sets of indices for early, medium and late M dwarfs
Spectral Type Spectral type distribution of CARMENCITA objects in the sample later type stars more interesting more late (and faint) targets observed with HRS only 14 stars later than M5.0
Spectral Type Spectral types of 79 CARMENCITA stars observed with two spectrographs FEROS: trend toward earlier types normalization issue?
Spectral Type Differences between calculated spectral types and literature FEROS and FEROS+X: trend toward earlier types CAFE and HRS: no trend only 4 stars with difference > 1 subtype
Spectral Type Summary: bad results for non-carmencita stars because only spectral indices sensitive for M dwarfs were used trend toward earlier spectral types for FEROS spectra typical differences to literature values 1 subtype
Activity pseudo-equivalent width of the Hα line: negative pew: visual check whether Hα is in emission magnetic activity strength: spectral type used to estimate T eff for χ(t eff )
Activity pew(hα) of 79 CARMENCITA stars observed with two spectrographs some significant outliers significant differences for 42 of 362 stars observed more than once (including stars observed with one spectrograph) possibly true variation; no correlation of variation with pew(hα) or SpT
Activity Comparison of results for CARMENCITA objects with literature higher values from Lep13, lower values from AF15 outliers possibly caused by true variation no correlation of differences with pew(hα) or SpT AF15: Alonso-Floriano et al. (2015); Lep13: Lépine et al. (2013); MR14: Martínez-Rodríguez (2014); PMSU: Palomar/Michigan State University Survey
Activity Fraction of active stars per spectral type 138 active CARMENCITA stars (29% of our sample) increasing fraction for later spectral types small sample of M5 or later stars [West et al. (2008)] late M dwarfs are active for a longer period of time (Hawley et al., 1996) and therefore more likely still active when observed
Activity Magnetic activity strength of individual stars and median (circles) per spectral type activity strength increases with spectral type for M0.0-M4.5 (except M2.5) few data points for SpT earlier than M2.0 and later than M4.5
Activity increasing activity related to faster rotation [Reiners et al. (2012)]
Activity Summary: variations of Hα emission for 42 stars, possibly true variability 29% of CARMENCITA stars identified as active fraction of active stars and median activity strength increase with the spectral type
Summary reduction of 256 CAFE spectra and analysis of 1700 CAFE, FEROS and HRS spectra of 480 CARMENCITA objects and 41 other stars radial velocity measurements with ~1 km s -1 accuracy 33 new spectroscopic binary candidates spectral types with 1 subtype accuracy magnetic activity strength of 138 CARMENCITA stars
References Alonso-Floriano, F. J., Morales, J. C., Caballero, J. A et al. 2015, A&A, 577, A128 Covey, K. R., Ivezic, Ž., Schlegel, D. et al. 2007, AJ, 134, 2398 2417 Hawley, S. L., Gizis, J. E. & Reid, I. N. 1996, AJ, 112, 2799 Lamert, A. 2014, MSc thesis, Georg-August-Universität Göttingen, Germany Lépine, S., Hilton, E. J., Mann, A. W. et al. 2013, AJ, 145, 102 Martínez-Rodríguez, H. 2014, MSc thesis, Universidad Complutense de Madrid, Spain Newton, E. R., Charbonneau, D., Irwin, J. et al. 2014, AJ, 147, 20 Piskunov, N. E. & Valenti, J. A. 2002, A&A, 385, 1095 1106 Quirrenbach, A., Amado, P. J., Caballero, J. A. et al. 2014, Proc. SPIE, 9147 Reid, I. N., Hawley, S. L. & Gizis, J. E. 1995, AJ, 110, 1838 Reiners, A., Joshi, N. & Goldman, B. 2012, AJ, 143, 93 West, A. A., Hawley, S. L., Bochanski, J. J. et al. 2008, AJ, 135, 785 795 Zechmeister, M., Anglada-Escudé, G. & Reiners, A. 2014, A&A, 561, A59